Experimental analysis of conformal cooling in SLM produced injection moulds: Effects on process and product quality

Abstract

In an injection moulding process, the cooling step takes up to 50% or more of the total cycle time. Therefore, any reduction of the cooling time directly results into an increase of the production rate. Furthermore, products are often rejected because of defects such as warpage or sink marks. The cause of these defects is often an unevenly distributed cooling in the mould due to complex product or mould shapes. A solution for both problems is Conformal Cooling, a technique in which the cooling channels are designed to follow the contour of the mould cavity to obtain an optimal cooling. These often curved cooling channels are difficult or even impossible to produce with conventional techniques such as milling, drilling and EDM. The recent development of the Selective Laser Melting (SLM) 3D printing technology can be used to overcome these limitations. In a previous work [1] the cooling channels of an existing mould to produce sorting trays were assessed and redesigned to achieve a conformal cooled mould. A mould cavity and insert were provided with these cooling channels by means of the SLM technique. In this work the performance of the conformal cooled mould is compared with the original mould based on process characteristics and product measurements. In particular the start-up losses, mould temperature during the cycle, cycle time and product warpage are assessed.